Thistle surpasses spurge

Canada thistle replaces leafy spurge as North Dakota’s scourge

June 17, 2008

Canada thistle is now North Dakota’s most widespread noxious weed with slightly more than 1 million acres across the state infested, surpassing leafy spurge, which affects 861,000 acres, according to the N.D. Department of Agriculture.

Reports came from data received from North Dakota’s county and city weed boards and land managers. Agriculture Commissioner Roger Johnson released the figures from the 2007 Noxious Weed Survey earlier this month to mark the start of Noxious Weed Awareness Month, proclaimed by Gov. John Hoeven.

“This is based on data from county weed officers, which is fairly accurate,” said Ward County Weed Control Officer Derrill Fick. “We use GPS tracking to get the numbers.”

Fick said leafy spurge, although still a prominent force along the state’s cropland, hillsides and shorelines with its pale yellow flower, has receded in recent years, due largely in part to awareness, integrated control strategies and good management.

In Ward County, flea beetles, natural predators of leafy spurge, have reduced the bluish-green plant to the second-most noxious weed behind Canada thistle.

“Leafy spurge has dropped dramatically in recent years,” Fick said. “The flea beetles would like better weather. It needs to be warmer and drier. They’re still working, but they’re harder to find.”

Typically, the beatles work in areas that can’t be reached by machinery, such as in draws and on sharp ridges.

“Weed control efforts in North Dakota have focused on leafy spurge for many years,” Johnson said. “In particular, the biological control program has been very successful in reducing spurge infestations.”

In addition, the county cost-shares on a couple of chemicals that have helped control leafy spurge and other weeds in open areas. Certified applicators may obtain Tordon at 25 percent of the original cost, which turns out to be about $25 a gallon.

Plateau, a chemical geared toward eradication of leafy spurge, is also cost-shared, but still costs the applicator about $70 a gallon, according to Fick.

Absinth wormwood is another noxious weed that should be monitored closely, Fick said. That invasive perennial, which can grow up to 4 feet tall, appears to be spreading in North Dakota.

“We have to watch out,” Fick said. “There’s more out there than people believe. It can invade any disturbed soil.”

Noxious weed month exists mostly as an awareness campaign, according to Fick, to let people know that any number of weeds, especially Canada thistle and leafy spurge, cut into farm and ranching profits.

In fact, recent cow/calf pair research indicates that nutrients and moisture are lost from beneficial plants with the onset of noxious weeds.

Especially with Canada thistle, livestock will not graze near it because of the prickly leaves and stems. But there are options to control the prickly thistle.

The South Dakota Department of Agriculture, Colorado State University and Penn State University have been using several methods of biological control on Canada thistle since 1997. Among them, the gall fly, seed head weevil, foliage feeder and stem mining weevil.

The stem mining weevil moves from the underside of early leaves in the spring, burrows into the stem and later exits, collapsing the plant at the crown.

“The larvae feed on the inside of the stem,” said N.D. Department of Agriculture Noxious Weed Specialist Blake Schaan. “The gall fly is used in conjunction with the stem mining weevil.”

Schaan said the biological control has been very successful in and around Bowman-Haley Dam and that the weevils have been introduced in numerous counties across the state. The first releases occurred in 2004, according to Schaan.

Maintaining turf density is also a good option in controlling Canada thistle, according to Colorado State University, since alfalfa and some grasses compete well against Canada thistle.

Finally, 2, 4-D, Tordon, Curtail and Banvel are all considered effective against Canada thistle.

With absinth wormwood, livestock can actually control its spread. Sheep will readily graze absinth wormwood, which is said to have 25 percent crude protein and a sage-like taste.

Angora goats have been used in Foster County to knock down and control leafy spurge.

But the weeds aren’t limited to farms and ranches. They can also be problematic to urban residents.

Fick often uses the analogy of purple loosestrife. Once a decorative plant, the invasive weed took control along the Souris River banks and now landowners work each summer to rid their property of the invader.

“According to the North Dakota Century Code, anyone with noxious weeds on their property needs to control them,” Fick said. “It’s up to them to manage the problem.”

Johnson said noxious weeds cost North Dakota tens of millions of dollars annually in lost agricultural production and control expenses.

“I have asked my staff to work with our county and other government agency partners to develop a measurement system that we would all use to accurately report noxious weed infestations,” he said. “We all need to be on the same page when we identify an acre of noxious weeds.”

Article Photos

Marvin Baker/MDN •

Ward County weed control officer Derrill Fick examines Canada thistle plants near the State Fairgrounds Monday. Canada thistle is now North Dakota’s most widespread noxious weed, according to survey data from the state’s 53 counties.

Marvin Baker/MDN •

Leafy spurge, which is no longer North Dakota’s most widespread noxious weed, blooms on a south Minot hillside Monday.

Marvin Baker/MDN •

Absinth wormwood is an invasive weed that tends to take over soil that is disturbed in any way. Interestingly, sheep readily graze this perennial, which is said to have 25 percent crude protein.

Fact Box

New county guidelines BISMARCK – County weed boards have new guidelines, forms and tags to help them conduct inspections of forage, gravel, scoria and sand for noxious and invasive weeds. “Last March, the North Dakota Department of Agriculture sat down with county weed boards, government land managers and private citizens to discuss the need for a program,” said Agriculture Commissioner Roger Johnson. “A committee was formed to develop a program. The new guidelines and associated materials were developed with the advice of the committee and the attorney general’s office.” Johnson said guidelines are based on standards established by the North American Weed Management Association for inspecting forage and on state and county weed lists for inspecting gravel, scoria and sand surface mining operations. A new orange, dated tag has been developed to mark inspected forage. Only a county weed board can certify inspectors. NDDA will no longer certify private individuals as forage inspectors. Inspector certification under the previous program has been rescinded, and recertification has been discontinued. Johnson said inspection of forage, gravel, scoria and sand is an important component of noxious and invasive weed control, and that many states have statewide inspection programs. “I hope the 2009 Legislature will take up the matter,” Johnson said. “Since counties are under no obligation to have an inspection program, a statewide program, like those in other midwestern and western states, would probably be best for North Dakota.”– Marvin Baker